Preliminary studies on beagle dogs have identified a retinopathy associated specifically with Vitamin E deficiency. The retinopathic changes include disruption and swelling of the photoreceptor outer segments and a buildup of autofluorescent pigment within the pigment epithelium cells. With time there is a total loss of photoreceptors and appearance of autofluorescent pigment in all retinal layers. The disease appears to progress from the central retina toward the periphery with the tapetal area more fully involved. There is an absence of the ERG by 3 months after weaning onto the deficient diet. The proposed research is designed to characterize the development and progression of the retinopathy from weaning using a physiological, histological and biochemical protocol. This will involve periodic testing of visual function using the ERG and EOG; and biochemical analysis of both blood and tissue for Vitamin E, selenium, taurine, and other relevant substances. A 2 X 2 factorial study will be employed using Vitamin E and selenium as deficiency factors. Selenium is included because of its role as an antioxidant precursor. Experiments to examine any interactions between Vitamin E and selenium, and taurine will also be done. Other experiments will: 1. Attempt to reverse or halt the retinopathy by subsequent replacement of Vitamin E in the diet. 2. Attempt to produce retinopathy in older animals previously maintained on normal Vitamin E diet. 3. Examine more thoroughly the loss of the ERG and test whether other antioxidants can prevent its loss. 4. Look for any effects of ambient light on the development or progress of the retinopathy by maintaining Vitamin E deficient dogs in both light and total darkness. The role of Vitamin A in producing the retinopathy will be examined.